The present invention relates to a method for manufacturing a wheel-supporting hub unit for supporting wheels of a vehicle on a suspension of the vehicle in a freely rotatable manner and a pressing mold for manufacturing same hub unit.
The wheels of the vehicle are supported on the suspension by the wheel-supporting hub unit. FIGS. 9A and 10 show an example of the wheel-supporting hub unit for supporting the wheels of the car (rear wheels of a FR car, front wheels of a FF car, all wheels of a 4WD car) on the suspension of the car, which is disclosed in Japanese Patent Unexamined Publication No.Hei 11-5404. In an outside end portion of an outer peripheral surface of a hub 2 forming the present wheel-supporting hub unit, there is disposed a flange 3. Here, a term xe2x80x9couterxe2x80x9d side means a side of the hub 2 that is near to outside the car in the width direction of the car in a state where the hub 2 is assembled to the car. In FIGS. 9A and 10, the term xe2x80x9couterxe2x80x9d side means the left side. On the other hand, the side of the hub 2 that is near to the center of the car in the width direction of the car is referred to as a xe2x80x9cinnerxe2x80x9d side. In FIGS. 9A and 10, the xe2x80x9cinnerxe2x80x9d side means the right side. In the middle portion of the outer peripheral surface of the hub 2, there is formed an inner raceway 4 which corresponds to a first inner raceway. In the inside end portion of the outer peripheral surface of the hub 2, there is formed a small-diameter stepped portion 5. An inner ring 6 includes another inner raceway 4 corresponding to a second inner raceway in its outer peripheral surface.
In FIG. 9B, as the same as above structure of the wheel supporting hub unit, in the inside end portion of the outer peripheral surface of the hub 2, there is formed a small-diameter stepped portion 5. An inner ring 6 includes inner raceway 4 corresponding to a first inner raceway and a second inner raceway in its outer peripheral surface. In FIGS. 9A, 9B and 10, the inner ring 6 is fitted with the outer surface of the small-diameter stepped portion 5, and the inside end face of the inner ring 6 is held by a caulking portion 7 formed in the inside end portion of the hub 2. The inner ring 6 is held by and between the caulking portion 7 and a stepped surface of the small-diameter stepped portion 5, thereby the inner ring 6 is fixed to the hub 2.
On the periphery of the hub 2, there is disposed an outer ring 8 in such a manner that it is concentric with the hub 2. In the inner peripheral surface of the outer ring 8, there are formed a pair of outer raceways 9, 9 corresponding to the first and second inner raceways.
Between the outer raceways 9, 9 and the inner raceways 4, 4, there are disposed rolling elements 10, 10 respectively two or more in number. In the illustrated embodiment, as the respective rolling elements 10, 10, there are used balls, however, in the case of a wheel-supporting hub unit for a car which is large in weight, taper rollers may also be used as the rolling elements.
Further, the hub 2 is formed in a cylindrical shape. In the inner peripheral surface of the hub 2, there is formed a female spline portion 11. On the female spline portion 11, there is disposed a constant-velocity joint 12. A drive shaft 13 includes a male spline portion formed in its outer peripheral surface and is inserted into the constant-velocity joint 12. A nut 14 is threadedly engaged with the leading end portion of the drive shaft 13. A stepped portion 15 is formed in the base end portion of the drive shaft 13. The inside end face of the nut 14 is contacted with the outside end face of the hub 2. The stepped surface 16 of the stepped portion 15 is contacted with the inside end face of the caulking portion 7 formed in the inside end portion of the hub 2. In this contact state, by fastening the nut 14, the hub 2 can be connected to the drive shaft 13. In the inside end face of the caulking portion 7, a flat portion 17 is formed to secure a contact area of the caulking portion 7 with respect to the stepped surface 16. The flat portion prevents the contact area from being deformed elastically and collapsing through plastic deformation.
In the outer peripheral surface of the outer ring 8, there is formed an outwardly-facing flange-shaped mounting portion 18. To assemble the above-structured wheel-supporting hub unit 1 to the car, the outer ring 8 is fixed to a suspension through the outwardly-facing flange-shaped mounting portion 18, and the wheels of the car is fixed to the flange 3. As a result of this, the wheels can be rotatably supported on the suspension. Alternatively, by driving the drive shaft 13 of the constant-velocity joint 12 rotationally through a rotation transmission shaft (not shown) with its base end portion connected to a differential gear (not shown), the hub 2 and the wheels fixed to the hub 2 can be driven or rotated.
When forming the caulking portion 7 in the inside end portion of the hub 2 so as to be shown the conventional structure in FIGS. 9A, 9B and 10, a cylindrical portion 19 formed in the inside end portion of the hub 2 is strongly pressed by a pressing mold. Then, the cylindrical portion 19 is plastic deformed outwardly in the diameter direction thereof. In this case, to the cylindrical portion 19, there are applied not only a force going outwardly in the diameter direction but also a large force going outwardly in the axial direction. Further, in the final stage of such working or plastic deforming operation, a force that goes inwardly in the diameter direction is also applied to the cylindrical portion 19. There is a possibility that, of these three kinds of forces, due to the two forces respectively going outwardly in the axial direction and going inwardly in the diameter direction, a part of the cylindrical portion 19 can be bulged and deformed inwardly in the diameter direction. In a case that the part of the cylindrical portion 19 is deformed inwardly in the diameter direction, there is a possibility that the drive shaft 13 of the constant-velocity joint 12 cannot be inserted into the female spline portion 11 formed in the central portion of the hub 2.
Further, there is another possibility that the fitted portion between the inner peripheral surface of the inner ring 6 and the outer peripheral surface of the cylindrical portion 19 can provide a clearance-fit in a part.
In a case that the fitted state provides such clearance-fit, a phenomenon called xe2x80x9ccreepxe2x80x9d, where the inner ring 6 rotates with respect to the hub 2, is easy to occur. In the case of the creep occurring, as the wheel-supporting hub unit 1 is used for a long period of time, unfavorably, the respective peripheral surfaces forming the above-mentioned fitted portion are worn. Further, a rickety motion is thereby easy to occur in the fitted portion. Especially, in a case that the axial length of the cylindrical portion 19 is large, there is a possibility that the inside diameter of a part of the cylindrical portion 19 can be reduced. The part of the cylindrical portion 19 is a considerable portion of the outer peripheral surface of the cylindrical portion 19, that is opposed to the inner peripheral surface of the inner ring 6. In such case, as the above-mentioned creep is easy to occur, it is necessary to prevent the diameter of the cylindrical portion 19 from reduce, with the working operation for forming the caulking portion 7.
The above-mentioned problem, that the drive shaft 13 cannot be inserted into the female spline portion 11, is a problem peculiar to a wheel-supporting hub unit for the drive wheels. However, the lowered support strength of the inner ring 6 caused by the occurrence of the clearance-fit can occur not only in a wheel-supporting hub unit for drive wheels but also in a wheel-supporting hub unit for coupled driving wheels (the front wheels of an FR car, and the rear wheels of an FF car).
The present invention aims at eliminating the above-mentioned drawbacks found in the conventional method for manufacturing a wheel-supporting hub unit and the conventional pressing mold for manufacturing such a hub unit. Accordingly, it is an object of the invention to provide a method for manufacturing a wheel-supporting hub unit and a pressing mold for manufacturing such a hub unit, which can prevent the diameter of a cylindrical portion formed in the inside end portion of a hub from being reduced in the working operation for forming a caulking portion.
In order to accomplish the object above, the following mean are adopted. According to the present invention, there is provided method for manufacturing wheel-supporting hub unit and pressing mold for manufacturing same hub unit. The method according to the first aspect of the invention, for example, similarly to the previously described conventional wheel-supporting hub unit shown in FIGS. 9A, 9B and 10, comprises a hub, a first inner raceway, a stepped portion, an inner ring, an outer ring, and a plurality of rolling elements.
Of these components, the hub includes a flange for supporting and fixing wheels in the outer peripheral surface of its outside end portion.
The first inner raceway is formed in the outer peripheral surface of the middle portion of the hub directly or through the inner ring disposed separately from the hub.
The stepped portion is formed in the inside end portion of the hub and has a smaller outside diameter dimension than that of the portion where the first inner raceway is formed.
The inner ring includes a second inner raceway formed in its outer peripheral surface and is fitted with the stepped portion.
The outer ring includes, in its inner peripheral surface, a first outer raceway opposed to the first inner raceway and a second outer raceway opposed to the second inner raceway, while the outer ring is not rotatable even when it is in use.
Further, the rolling elements are interposed between the first inner raceway and first outer raceway as well as between the second inner raceway and second outer raceway, respectively in two or more in number.
The inner ring fitted with the stepped portion is connected and fixed to said hub in such a manner that it is held toward a stepped surface of the stepped portion by a caulking portion. The caulking portion is formed by plastic deforming which caulks and spreads a cylindrical portion outwardly in the diameter direction of the hub. In this bout, the cylindrical portion is formed in the inside end portion of the hub in such a manner that the inside end portion of the cylindrical portion is projected inwardly from the inner ring fitted with the outer surface of the stepped portion.
According to the method for manufacturing the above-structured wheel-supporting hub unit, as a pressing mold for plastic deforming caulks and spreads a cylindrical portion outwardly in the diameter direction, there is used a pressing mold including a cylindrical projecting portion which can be freely pushed into the cylindrical portion. Therefore, a part of the cylindrical portion is superimposed on the inner peripheral surface of the inner ring in the diameter direction. In addition, the part is supported by the cylindrical projecting portion to prevent the cylindrical portion from shifting toward the inside diameter side. That is, the caulking portion is formed in this manner.
The pressing mold for manufacturing the wheel-supporting hub unit according to the second aspect of the invention is used when enforcing a wheel-supporting hub unit manufacturing method according to the first aspect of the invention. That is, the present pressing mold can be butted against the leading end face of the above-mentioned cylindrical portion to thereby apply to the cylindrical portion not only a force moving in the axial direction but also a force moving outwardly in the diameter direction. The pressing mold for manufacturing a wheel-supporting hub unit, according to the second aspect of the invention, includes a cylindrical projecting portion slidable into the inside of the cylindrical portion formed in the central portion of the leading end face thereof, and an annular-shaped recessed portion formed in the periphery of the cylindrical projecting portion so as to enclose the entire periphery of the cylindrical projecting portion. The outer peripheral surface of the cylindrical projecting portion can be contacted with the inner peripheral surface of the cylindrical portion in such a manner that the annular-shaped recessed portion is butted against the inside end portion of the cylindrical portion to thereby plastic deform the cylindrical portion.
Preferably, the operation to plastic deform (caulk and spread) the cylindrical portion outwardly in the diameter direction to form the caulking portion by the present manufacturing pressing mold may be carried out by oscillating and caulking the cylindrical portion. In this operation, more preferably, in a portion of the pressing mold, as the annular-shaped recessed portion forms the caulking portion, there may be used an annular-shaped recessed portion which has the following section shape. That is, said annular-shaped recessed portion further comprised a bottom surface portion disposed in the periphery of its deepest portion, an inside-diameter-side curved surface portion having a concave-arc-shaped section which continues smoothly with an outer peripheral part of said bottom surface portion or intersects said bottom surface portion at an outer part thereof, a conical-concave-shaped inclined surface portion having a linear-shaped section which continues smoothly with an outer peripheral part of said inside-diameter-side curved surface portion or intersects said inside-diameter-side curved surface portion at an outer part thereof and an outside-diameter-side projecting surface portion having a convex-arc-shaped section which continues smoothly with an outer peripheral part of said inclined surface portion or intersects said inclined surface portion at an outer part thereof. These three surface portions may be concentric with one another. Also, as assuming that there is a virtual straight line connecting the oscillation center of the pressing mold with the boundary position between the inside-diameter-side curved surface portion and the inclined surface portion, an angle formed between the inclined surface portion and a perpendicular line with respect to the virtual straight line is defined as a tangent angle. Further, an intersection angle between the present virtual straight line and a virtual plane portion extending at right angles to the oscillation center axis of the pressing mold is defined as an offset angle. Under these conditions, the tangent angle is regulated to the range from 13xc2x0 to (an angle defined by subtracting said offset angle from 90xc2x0).
[Operation]
The operation to support wheels on a suspension rotatably, which is carried out by a wheel-supporting hub unit manufactured by the above-structured wheel-supporting hub unit manufacturing method according to the invention, is similar to the operation of the conventional wheel-supporting hub unit shown in FIGS. 9A, 9B and 10.
Especially, in the case of the wheel-supporting hub unit manufacturing method according to the invention, since the caulking portion is formed by an oscillating and caulking operation while holding the inner peripheral surface of the cylindrical portion by the outer peripheral surface of the cylindrical projecting portion, the cylindrical portion can be prevented from shifting in part inwardly in the diameter direction and the shape of the caulking portion can be regulated strictly as desired. Therefore, there is eliminated a fear that the support strength of the inner ring by the caulking portion can be short. And, in the case of a wheel-supporting hub unit for drive wheels, there is no possibility that the operation to insert the drive shaft into the inside diameter side of the hub can be troublesome. Also, the fitted portion between the outer peripheral surface of the cylindrical portion and the inner peripheral surface of the inner ring can be maintained in a close fit state, thereby being able to prevent the occurrence of a creep phenomenon in which the inner ring can rotate with respect to the cylindrical portion.
Especially, in case where the tangent angle of the inclined surface portion formed in the annular-shaped recessed portion of the pressing mold is regulated to the range from 13xc2x0 to (an angle defined by subtracting said offset angle from 90xc2x0), not only the occurrence of burrs in the outer peripheral edge portion of the caulking portion but also the occurrence of cracks in the caulking portion can be prevented, which makes it possible to provide a caulking portion of better quality.